My 400E has been running rough as of late.
Today I had a emissions check and almost failed. HC reading was 193 ppm.
CO2 reading was 14.59 %.

Can't really pinpoint symptoms other than every thing seems pretty normal.

Gas mileage not unusally high, Temp runs around 80c during all types of driving.

Issue is that under certain times when I pull up to a stop light. The engine feels like it has lost 3 cylinders and stumbles/ chugs hard. The taletale sulphur odor is omnipresent. 90% of the time the car runs like a champ. Smooth idle, plenty of power,etc. I can shut the car off when running rough then start back up and it returns to normal. LAst month I figured it needed a tune up and changed plugs and cap and rotors. Ran better but problem persistend.

The sulphor/rotten egg smell is noticable while driving. (i.e fumes come back in the S/R opening with side windows closed.

I know something is wrong but need a hint as to where to start.

Any ideas?

Thanks, Mike
92 400E